88 420SEL transmission problem

[william.wood]

i aquired this beaty 8 months ago , trans fluid was dark and murky / not clear. changed fluid 2X so as to get it clean and clear again. and have only put on 430 miles since did not want to drive in snow and salt as it had no rust. so i drive it sparingly 1X-2X a week .. it was a clear dry day 30F so decided to take her out to a doctors appt. 1 mile from home the trans started howling and acting tight .... pulled into lot to turn around... NO REVERSE! .... on the way back home trans was slipping in high gear had to downshift and go low throttle to keep from slipping .. trans now has a whine in it that getts even louder between shifts in the driveway ...
fluid level is still good ... seafoam trans-cure did nothing.
NOW WHAT?